<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    手机号：<input type="number"> <button>发送</button>
    <script>
        var btn = document.querySelector('button');
        var time = 3; // 剩下的秒数
        btn.addEventListener('click', function() {
            btn.disabled = true;
            btn.innerHTML = '剩余' + time + '秒';
            var timer = window.setInterval(function() {
                if (time == 0) {
                    clearInterval(timer);
                    btn.disabled = false;
                    btn.innerHTML = '发送';
                    time = 3;
                } else {
                    btn.innerHTML = '剩余' + time + '秒';
                    time--;
                }
            }, 1000);
        });
    </script>
</body>

</html>